The present invention relates to a power supply unit for generating voltage, a semiconductor device for controlling the power supply unit, and a wireless communication device to which the power supply unit is applied and, more specifically, to a technique effectively applied to a power supply unit having a function of varying voltage to be output.
In recent years, a wireless power supply system for supplying power in a noncontact (wireless) manner is being spread. For example, a wireless power supply system of an electromagnetic induction method using electromagnetic induction between coils arranged apart from each other is included by a transmission-side device transmitting power and a reception-side device receiving the transmitted power, and a small-sized portable terminal device as the reception-side device can, for example, charge a battery on the basis of power received. As a standard related to the noncontact communication technique of transmitting information by radio, NFC (Near Field Communication) is known. A small portable terminal device conformed to the NFC standard
In recent years, a wireless power supply system performing power transmission and communication for transmitting information while switching them by commonly using an antenna used for NFC and an antenna used for wireless power transmission of an electromagnetic resonance method is being developed. At the time of performing communication for transmitting information, a transmission-side device in such a wireless power supply system generates a drive signal having relatively small amplitude, by a drive circuit and transmits a signal by driving the antenna. At, the time of transmitting power the device generates a drive signal having a large amplitude by the drive circuit and transmits a signal by driving the antenna. To generate drive signals having different amplitudes for the power transmission and information communication by a single drive circuit in the transmission-side device, for example, a power supply unit capable of varying the power supply voltage to be supplied to the drive circuit is necessary.
As the power supply unit, conventionally, a switching regulator and a series regulator are known. In addition, a power supply unit for supplying power to a load while selectively switching an output from a switching regulator and an output from a series regulator is known. For example, patent literature 1 discloses a technique related to a power supply unit realizing reduced current consumption at the time of a light load by switching any of output voltages of an LDO (Low Drop Out) regulator as a linear regulator and a switching regulator in accordance with load current and outputting the voltage.